1. Field of the Invention
The present invention relates to a process and an apparatus for producing molten metal (which term includes metal alloys), in particular although by no means exclusively iron, from ferrous material, such as ores, partly reduced ores and metal-containing waste streams.
The present invention relates particularly to a molten metal bath-based direct smelting process and an apparatus for producing molten metal from a ferrous material.
2. Description of Related Art
One known molten bath-based direct smelting process for producing molten ferrous metal is the DIOS process. The DIOS process includes a pre-reduction stage and a smelt reduction stage. In the DIOS process ore (−8 mm) is pre-heated (750° C.) and pre-reduced (10 to 30%) in fluidised beds using offgas from a smelt reduction vessel which contains a molten bath of metal and slag, with the slag forming a deep layer on the metal. The fine (−3 mm) and coarse (−8 mm) components of the ore are separated in the pre-reduction stage of the process. Coal and pre-heated and pre-reduced ore (via two feed lines) are fed continuously into the smelt reduction furnace from the top of the furnace. The ore dissolves and forms FeO in the deep layer of slag and the coal decomposes into char and volatile matter in the slag layer. Oxygen is blown through a specially designed lance that improves secondary combustion in the foamed slag. Oxygen jets burn carbon monoxide that is generated with the smelting reduction reactions, thereby generating heat that is transferred to the molten slag. The FeO is reduced at the slag/metal and slag/char interfaces. Stirring gas introduced into the hot metal bath from the bottom of the smelt reduction vessel improves heat transfer efficiency and increases the slag/metal interface for reduction. Slag and metal are tapped periodically.
Another known direct smelting process for producing molten ferrous metal is the AISI process. The AISI process also includes a pre-reduction stage and a smelt reduction stage. In the AISI process pre-heated and partially pre-reduced iron ore pellets, coal or coke breeze and fluxes are top charged into a pressurised smelt reactor which contains a molten bath of metal and slag. The coal devolatilises in the slag layer and the iron ore pellets dissolve in the slag and then are reduced by carbon (char) in the slag. The process conditions result in slag foaming. Carbon monoxide and hydrogen generated in the process are post combusted in or just above the slag layer to provide the energy required for the endothermic reduction reactions. Oxygen is top blown through a central, water cooled lance and nitrogen is injected through tuyeres at the bottom of the reactor to ensure sufficient stirring to facilitate heat transfer of the post combustion energy to the bath. The process offgas is de-dusted in a hot cyclone before being fed to a shaft type furnace for pre-heating and pre-reduction of the pellets to FeO or wustite.
Another known direct smelting process, which relies on a molten metal layer as a reaction medium, and is generally referred to as the HIsmelt process, is described in International application PCT/AU96/00197 (WO 96/31627) in the name of the applicant.
The HIsmelt process as described in the International application comprises:                (a) forming a bath of molten metal and slag in a vessel;        (b) injecting into the bath:                    (i) metalliferous feed material, typically metal oxides; and            (ii) a solid carbonaceous material, typically coal, which acts as a reductant of the metal oxides and a source of energy; and                        (c) smelting the metalliferous feed material to metal in the metal layer.        
The HIsmelt process also comprises injecting oxygen-containing gas into a space above the bath and post-combusting reaction gases, such as CO and H2, released from the bath and transferring the heat generated to the bath to contribute to the thermal energy required to smelt the metalliferous feed materials.
The HIsmelt process also comprises forming a transition zone in the space above the nominal quiescent surface of the bath in which there is a favourable mass of ascending and thereafter descending droplets or splashes or streams of molten materiel which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.
The HIsmelt process as described in the international application is characterised by forming the transition zone by injecting a carrier gas, metalliferous feed material, and solid carbonaceous material into the bath through a section of the side of the vessel that is in contact with the bath and/or from above the bath so that the carrier gas and the solid material penetrate the bath and cause molten material to be projected into the space above the surface of the bath.
The HIsmelt process as described in the International application is an improvement over earlier forms of the HIsmelt process which form the transition zone by bottom injection of gas and/or carbonaceous material into the bath which causes droplets and splashes and streams of molten material to be projected from the bath.